Because I'm listening to this right now (while coding at work): 

Artist: Slayer
Venue: Sports Arena
Location: San Diego, CA
Date: 10/12/88

Source: Unknown Audience (LOSSLESS) > CDR > WAV >
GoldWave 5.06 ("Time Warp" effect @ 95.2 ratio) >
Sonic Foundry Sound Forge 6.0 (To EQ) > WAV > SHN

Setlist

1.  South of Heaven
2.  Raining Blood
3.  Silent Scream
4.  At dawn they Sleep
5.  Read Between the Lies
6.  Mandatory Suicide
7.  Behind the Crooked Cross
8.  Spill the Blood
9.  Live Undead
10. Angel of Death

Comments: This is them opening for Judas Priest. This version has the correct
speed playback. The versions mainly in circulation are at a very high speed
playback, so now it's all taken care of. Also cleaned up the clarity and sound
quality with slight EQing. Enjoy!

I was actually at this show. And someone in the audience - sounds like on the floor towards the right side of the arena (since the right channel is louder) made a tape. 17 years later it finds its way onto the intarweb for trading…

ps. Thank Sassy for the Slayer revive - he prompted me to dig out my 19 year old Reign in Blood tape for him and Goatgirl to listen to.